🌐 Mailman 3 September 2016 - Python-list - python.org

Re: *args and **kwargs
by Smith Sept. 2, 2016

Sept. 2, 2016

> > After specifying a keyword argument, you may not then specify any > positional arguments. Hence the SyntaxError. > thanks a lot

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Re: *args and **kwargs
by alister Sept. 2, 2016

Sept. 2, 2016

On Fri, 02 Sep 2016 23:44:50 +1000, Ben Finney wrote: > Smith <smith(a)smith.com> writes: > >> I'm trying to understand the concept of * args and ** kwarg with >> python3 > > Welcome. Your questions are fine in this forum; but you may also want to > participate in our collaborative learning forum for Python beginners, > <URL:https://mail.python.org/mailman/listinfo/tutor>. > >> But I can not understand why I returns the error message "SyntaxError: >> positional argument follows the keyword argument" when I insert values. > > It's fairly simple (though it may not be obvious!): > >> In [23]: start(data="Fish",2,3,tox="tux") >> File "<ipython-input-23-eb9c3abb9941>", line 1 >> start(data="Fish",2,3,tox="tux") >> ^ >> SyntaxError: positional argument follows keyword argument > > Exactly. > > Note that this has nothing to do with how the function is defined; in > the definition of the function, parameters are neither positional nor > keyword. You name each of them, and you define an order for them; and > neither of those makes any of them “positional” or “keyword”. > > Rather, “positional argument and “keyword argument” are characteristics > of the arguments you *supply* in a particular call to the function. > > You have specified four arguments, in this order: > > * A keyword argument, ‘data="Fish"’. > * A positional argument, ‘2’. > * A positional argument, ‘3’. > * A keyword argument, ‘tox="tux"’. > > After specifying a keyword argument, you may not then specify any > positional arguments. Hence the SyntaxError. & the solution is to change the order of the definition def start( must_have,*args,**kwargs,data=none): -- Pretend to spank me -- I'm a pseudo-masochist!

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Re: Python slang
by Random832 Sept. 2, 2016

Sept. 2, 2016

On Wed, Aug 10, 2016, at 07:59, Dennis Lee Bieber wrote: > The use of = also has a long history... FORTRAN (where the comparison > was .EQ.), BASIC (granted, K&K required assignment to start with the > keyword LET, so the use of = was mainly a delimiter between target and > expression being assigned). Visual Basic actually uses = for both assignment and comparison *without* the Let keyword, it gets by on the fact that assignment is not an expression.

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urllib2 timeout not working - stalls for an hour or so
by Sumeet Sandhu Sept. 2, 2016

Sept. 2, 2016

Hi, I use urllib2 to grab google.com webpages on my Mac over my Comcast home network. I see about 1 error for every 50 pages grabbed. Most exceptions are ssl.SSLError, very few are socket.error and urllib2.URLError. The problem is - after a first exception, urllib2 occasionally stalls for upto an hour (!), at either the urllib2.urlopen or response.read stages. Apparently the urllib2 and socket timeouts are not effective here - how do I fix this? ---------------- import urllib2 import socket from sys import exc_info as sysExc_info timeout = 2 socket.setdefaulttimeout(timeout) try : req = urllib2.Request(url,None,headers) response = urllib2.urlopen(req,timeout=timeout) html = response.read() except : e = sysExc_info()[0] open(logfile,'a').write('Exception: %s \n' % e) < code that follows this : after the first exception, I try again for a few tries >

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C Python extension to export an Function
by Ganesh Pal Sept. 2, 2016

Sept. 2, 2016

Hi Team, Iam on python 2.7 and Linux. Iam pretty new to C Python extension , I was able to export few simple modules to python and it look like the cool thing to do , but Iam stuck for with a problem now , Iam not able to figure out how to export fun_addr_from_addr() to Python. I would need some suggestion on how to develop a C Python API for the below piece of code. 1. The end goal is to export fun_addr_from_addr(baddr, *baddr) to Python. Perhaps by creating a python wrapper for fun_bh_toblkoff() would help me ? Here is the sample example code. fun_toblkoff(dda_locn_t *locn, struct ifs_baddr *baddr, int *poff, int *psize) { if (dda_locnparm_get(locn) != OK) return FAIL; /* fill in baddr */ *baddr = dda_index_to_baddr(locn->idx); if (locn->flags & DLFLAG) locn->xoff = fun_addr_from_addr(baddr, *baddr); *poff = 0; *psize = _BSIZE; return OK; } So the primary challenge when writing a wrapper for a single function is figuring out how to get the arguments from Python form to C form, and how to get the result back to Python form. Regards, Ganesh

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Python 3 at Facebook
by Terry Reedy Sept. 1, 2016

Sept. 1, 2016

https://www.youtube.com/watch?v=nRtp9NgtXiA Jason Fried explains how he helped advance 'modern Python', 3.x, from 'impossible' in 2013 to the 'default for new code' today. -- Terry Jan Reedy

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Re: C Python extension to export an Function
by Christian Gollwitzer Sept. 1, 2016

Sept. 1, 2016

Hi Ganesh, Am 01.09.16 um 17:24 schrieb Ganesh Pal: > Thanks stefan and Gollwitzer , good to know there are many ways to do this > i.e via cython or SWIG but the C/Python API > <https://docs.python.org/2/c-api/> is probably the most widely used method > - not for it’s simplicity but for the fact that you can manipulate python > objects in your C code. I'm not sure you understood what SWIG or Cython do - they are not circumventing the C/Python API, they merely write some of the code for you (as a C file). With both you can add manually written C code if the generated code is insufficient, and you can also ship the generated code, so that SWIG or Cython are not needed to rebuild the module, unless the API of your C coded functions changes. > I want to use C/Python API <https://docs.python.org/2/c-api/> You may have good reasons to do it manually anyway, in this case look at the PyArg_ParseTuple and Py_BuildValue functions documented here https://docs.python.org/2/c-api/arg.html Christian

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Re: C Python extension to export an Function
by Pavel S Sept. 1, 2016

Sept. 1, 2016

If you're familiar with C++, I recommend to have a look at Boost::Python. Sample program: #include <boost/python.hpp> #include <iostream> void world() { std::cout << "hello world" << std::endl; } BOOST_PYTHON_MODULE( hello ) { using namespace ::boost::python; def( "world", &world ); } Usage: python -c "import hello; hello.world()"

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Issues with "twistd" in Twisted 16.4.0
by juraseg Sept. 1, 2016

Sept. 1, 2016

Hi all I couldn't find Twisted-specific group, so posting here. Recently Twisted 16.4.0 got released. Yesterday I've tried to upgrade it for my apps and got an error. I've created simple example, which demonstrates it. File service.tac: ---------------------------------------- # You can run this .tac file directly with: # twistd -ny service.tac import os from twisted.application import service, internet import mymodule application = service.Application("Demo application") ---------------------------------------- File mymodule.py: ---------------------------------------- def myfunction(asd): """ Stub function """ ---------------------------------------- If you try to run it with twistd -y service.tac you'll get an error: >>> Failed to load application: No module named mymodule The errors comes down to this: twistd script does not add current working directory to python path, so it fails to import any packages/modules from it. It works just fine on previous version (Twisted 16.3.2). The strange thing here is that it was working before just fine, and I did not find anything related to this in release notes (http://labs.twistedmatrix.com/2016/08/twisted-1640-released.html), except that twistd now is a Setuptools console script (which I honestly don't know how can affect python path). Any ideas?

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Re: C Python extension to export an Function
by Christian Gollwitzer Sept. 1, 2016

Sept. 1, 2016

Am 01.09.16 um 14:30 schrieb Ganesh Pal: > On Thu, Sep 1, 2016 at 12:32 PM, dieter <dieter(a)handshake.de> wrote: > >> Ganesh Pal <ganesh1pal(a)gmail.com> writes: >> >>> Iam pretty new to C Python extension , I was able to export few simple >>> modules to python and it look like the cool thing to do ... >> >> Maybe, it is a good idea to have a look at "cython". >> >> "cython" is a compiler. It translates Python code enhanced with >> special annotations into C. The annotations mostly tell the compiler >> that something ("object", "method", "function", ...) should be at "C" >> rather than "Python" level, thus avoiding much of Python's overhead >> and allows to do things possible in "C" but not in "Python". >> >> >> Developing safe "C" extensions for Python is difficult. You >> need some quite deep understanding of the Python-C interface >> and must be very careful to observe all requirements (especially >> those related to proper reference management). >> >> Developing "C" extensions with "cython" is much easier as >> "cython" hides many of the complexities and takes care of most >> requirements. >> > > Dear Dieter , > > Really appreciate the reply and your suggestion on trying to use "cython" > , but my whole idea of using "C" extension is to regular C codes . We > have bunch of C code that's already available and C -Python seems to suit > me better Yet another option is to try SWIG. SWIG is a special compiler, you feed C header files which declare your functions, and it writes the wrapper code for you. In simple cases (standa data types like int, float, string,...), it might be enough. In more advanced cases, you can add your wrappers as "typemaps". Christian

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